Since Joining madrid:
16/17 Calf Injury Apr 24, 2017 Jun 1, 2017 38 days, games missed: 8

16/17 Calf muscle strain Apr 13, 2017 Apr 20, 2017 7 days, games missed: 2

16/17 Ankle injury Nov 24, 2016 Feb 16, 2017 84 days, games missed: 17

16/17 Hip injury Sep 15, 2016 Sep 22, 2016 7 days, games missed: 2

15/16 Disrupted Calf Muscle Jan 18, 2016 Mar 3, 2016 45 days, games missed: 8

15/16 Muscle Injury Oct 19, 2015 Nov 5, 2015 17 days, games missed: 4

15/16 Muscle Injury Sep 17, 2015 Sep 28, 2015 11 days, games missed: 3

14/15 Hamstring Injury Oct 20, 2014 Oct 30, 2014 10 days, games missed: 3

13/14 Muscular problems Oct 3, 2013 Oct 17, 2013 14 days, games missed: 1
in the past 3 seasons, he has missed a total of 48 games
So roughly about 16 games a season on average, although not half a season like you say but still not good at all. That ankle injury is worrying to have missed 17 games during the 16/17 season. It is also likely that his calf injuries are down to that ankle injury niggling him. For someone who is as fast and powerful as him, this is a big risk factor as that is so much of his game.